Sensitive pick-up relay



United States Patent [72] lnventor William E. Shaffer Rochester, N.Y.[21 Appl. No. 772,964 [22] Filed Nov. 4, 1968 [45] Patented Dec. 29,1970 [7 3] Assignee Stromberg-Carlson Corporation Rochester, N.Y. acorporation of Delaware [54] SENSITIVE PICK-UP RELAY 6 Claims, 4 DrawingFigs.

[52] US. Cl. 317/155.5, 179/18: 335/180 [51] Int. Cl 1101b 47/06 [50]Field ofSearch 317/137, 148.5,155, lS5.5;335/177,178, 180,268;179/18.8,l8 7,18.3A

[56] References Cited UNlTED STATES PATENTS 3,425,009 1/1969 Voight eta1. 335/177 RELAY MAIN l2 AUX.

Primary Examiner Lee T. Hix Assistant Examiner-William J. SmithAttorneys-Hoffman Stone and Charles C. Krowczyk ABSTRACT: An arrangementfor increasing the sensitivity of a relay or other electromechanicalactuator. l n the preferred case, an auxiliary winding is used in serieswith a switching transistor and the main winding. The auxiliary windingand transistor are shunted by a pair of normally open contacts of therelay. When an energizing voltage is applied, the transistor conducts,and the auxiliary winding contributes to the sensitivity of the relay.When the relay picks up, the auxiliary winding is shunted out of thecircuit, and the transistor is biased to cut off, effectivelyopen-circuiting the auxiliary winding and making it ineffective to delaysubsequent drop out of the relay when it is deenergized. An alternativearrangement omits the transistor, simply shorting the auxiliary windingwhen the relay picks up.

PATENTED [15029 mm SHEET 1 [IF 2 FIG. I

INVENTOR WILLIAM E. SHAFFER ATTORNEY I l l 'I TO I I i LINE 9? 90 93LINE G} FIG. 4

INVENT( m WILLIAM E. SHAFFER ATTORNILY sausmvs PICK-UP RELAY BRIEFSUMMARY This invention relates to a novel circuit arrangement forincreasing the sensitivity of a relay or the like, and, moreparticularly, but not exclusively, to a novel arrangement of the statedtype especially well adapted for use in connection with pulsing andbattery feed relays in telephone systems.

Relays used in telephone systems for detecting off-hook conditions atsubsets and for following dial pulses present problems, especially incases where they must work on line loops of relatively high resistancesuch as I900 ohms or higher. They are ordinarily connected across theline in series I with one side of a bridge transformer and the centralofiice battery. When the line loop resistance is high, very littlecurrent is available to operate the relay, and it must be highlysensitive if it is to pick up in response to'loop closure. Increasingsensitivity by the usual means such as by increasing the number of turnsin the relay winding results in delaying the release time so that oftenthe relay fails to follow dial pulses properly. I

Accordingly, one important object of the present invention is to providea circuit arrangement for increasing the sensitivity of a relay withoutsignificantly affecting its release characteristics.

Briefly, the invention contemplates the use of an auxiliary winding onthe relay core, and a switching arrangement for connecting the auxiliarywinding in series with the main winding during the initial applicationof an energizing voltage until the relay picks up, and then effectivelyopen circuiting the auxiliary winding until the relay releases so thatthe auxiliary winding does not delay the release. In an alternative formof the invention, for use where a significant delay is tolerable in therelease characteristic of the relay, the auxiliary winding is simply,short circuited by normally open contacts of the relay. In these cases,shunt loading of alternating current signals passing through the mainwinding may be minimized by connecting a diode in series with theauxiliary winding.

M DETAILED DESCRIPTION Representativeembodiments of the invention willnow be described in connection with the accompanying drawing, whereinr'FIG. 1 is a schematic circuit diagram of a relay arrangement accordingto a first embodiment of the invention;

FIG. 2 is a schematiccircuit diagram of a relay arrangement according toa modified form of the invention in a balanced configuration such aswould be used, for example, in many telephone systems;

FIG. 3 is a schematic circuit diagram of a relay arrangement accordingto a presently preferred embodiment of the invention for battery feedand pulsing in telephone service; and

' FIG. 4 is a schematic circuit diagram of another embodiment of theinvention for use where the relay is not required to follow rapid pulsesignals.

According to a first embodiment of the invention, as shown in FIG. 1, anauxiliary winding 10 is connected in a series circuit, which includesthe main winding 12 of a relay M, the emitter-to-collector current pathof an NPN transistor 16, a battery 18, a resistor 19, and a switch 20.The auxiliary winding 10 is connected between one terminal of the mainwinding 12 and the emitter of the transistor 16. The resistor 19 isconnected between the collector of the transistor I6 and the battery 18through the switch 20. A pair of normally open contacts R-I of the relayI4 are connected between the collector of the transistor I6 and thejunction between the auxiliary winding 10 and the main winding 12. Abase resistor 22 is connected between the base of the transistor 16 andthe junction between the two windings I and H2. The value of the baseresistor 22 is greater than the resistance value of the auxiliarywinding 10. Diodes 24 and 26 may be connected in series with the emitterand base, respectively, of the transistor 36 to protect the transistoragainst circuit transients and the application of reverse biasingvoltages. They are not essential to the circuit and in many cases may beomitted.

In operation, upon the initial application of an energizing voltage suchas, for example, occurs upon closing of the switch 20, the transistor 16is biased in its forward direction, and the auxiliary winding 10conducts in series with the main winding 12, thus providing highsensitivity icking up the relay. As soon as the relay picks up, itscorita R 1 close, connecting the collector of the transistor 16 to thejunction between the windings l0 and 12, thus cutting it off, andclosing a shunt path across the transistor 16 and the auxiliary winding10. The relay 14 remains held up by the main winding 12 only. Decay ofcurrent in the auxiliary winding 10 applies an added backbias across theemitter junction of the transistor 16, and, following decay of currentin the auxiliary winding, the base of the transistor 16 is held at thesame potential as its emitter, thus keeping the transistor cut off andthe auxiliary winding open circuited.

When the energizing circuit is thereafter opened to release the relay,the tendency of the auxiliary winding I0 to conduct in a parasitic modeapplies a reverse bias to the emitter junc tion of the transistor 16,and the current through the auxiliary winding 10 is held to a negligiblevalue so that it has no significant delaying effect upon the releasecharacteristics of the relay.

The embodiment shown in FIG. 2 is generally similar in principle to theone shown in FIG. 1, except that it is arranged for use in a balancedtelephone signalling circuit. The relay 23 shown therein includes twomain windings 25 and 27, respectively, and separate auxiliary windings30 and 31, respectively, each connected separately in series with itsownrespective transistor 32 and 33, respectively, and one of the mainwindings 25 and 27. In this case, because of the polarity of the appliedvoltages, one of the transistors 32 is of the PNP type and the other one33 is of the NPN type. The circuit operates Auxiliary resistors 36 and37, respectively, are shown connected between the emitters andcollectors of the respective transistors 32 and 33. These resistors areof relatively high value. They assist in biasing the transistors 32 and33 immediately upon closing of the switch 20 to insure promptness ofresponse. In many cases, depending upon the characteristics of thetransistors 32 and 33, and on the other parameters of the circuit, theauxiliary resistors 36 and 37 may be omitted.

The circuit illustrated in FIG. 3 is generally similar to the one shownin FIG. 2, except that the transistors 40 and 41 are on the battery sideof the relay for better protection against lightning and transienteffects in the subscribers lines.

As shown, the main windings 43 and 44, respectively, of the relay arearranged to be connected directly to the two leads 46 and 47 of thesubscribers line. They are shunted by respective diodes 49 and 50 inseries with limiting resistors 51 and 54, respectively. The transistors40 and 41, and the auxiliary windings 52 and 53 are in series betweenthe main windings 43 and 44, respectively, and the battery terminals 55and 56.

Normally open contacts 58 and 59 are connected respectively in shuntacross the auxiliary winding 52 and the transistor 40,"

and the auxiliary winding 53 and the transistor 41.

The auxiliary winding 52 is shunted by a voltage divider ineluding firstand second resistors 61 and 62 with a diode 64 connected between them.An exactly similar arrangement including resistors 66 and 67 and a diode69 shunts the other auxiliary winding 53. The bases of the transistors40 and 41 are connected to the respective diodes 64 and 69 in theshuntpaths through respective protective diodes 71 and 72. Diodes 74 and 75are respectively connected between the emitters and collectors of thetwo transistors 40 and ill, primarily to 7 protect the transistorsagainst lightning induced transients. Finally, capacitor 77 and 78 areconnected between the bases of the respective transistors 40 and 41 andthe respective battery terminals 55 and 56 for damping the effect oftransient voltage fluctuations. The capacitors 77 and 78 are shunted byrespective diodes 80 and 81, each in series with a limiting resister 83and 84.

The values of the various components of an actual circuit conforming tothe schematic circuit diagram of FIG. 3, which was built andsuccessfully tested under practical operating conditions were asfollows:

Resistance of the main windings 43 and 44 ohms each 205 Resistance ofthe auxiliary windings 52 and 53 .ohms each.. 135 Resistance of theshunt resistors 51 and 54 ohms eaeh 3, 300 Resistance of the firstvoltage divider resistors 61 and 66 hms each 680, 000 Resistance of thesecond voltage divider resistors 62 and 67 ohms each 20, 000 Capacity ofthe shunt capacitors 77 and 78 uf. each 0. 1 Resistance of the limitingresistors 83 and 84 ohms each 200 The circuit operated successfully toenable the relay to follow telephone dialing pulses over subscriber lineloops of various different characteristics and impedances up to 3000ohms.

The much simpler circuit shown in FIG. 4 is designed for use in caseswhere the relay need not follow rapid dialing pulses and a significantdelay can be tolerated in its release characteristic. The circuit isadvantageous where high sensitivity is required, but where theresistance of the relay winding, once it is picked up, must be held to alow value.

The circuit shown in FIG. 4 includes an auxiliary winding 90 connectedin series with one of the main windings 92 and 93, and shunted by a pairof normally open contacts 95 of the relay. A diode is connected inseries with the auxiliary winding 90 to block low level alternatingcurrent signals.

Pulsing and battery feed relays as used in telephony are usuallyconnected across the subscribers lines, shunting the so-called speechsignals. It is, therefore, important that they present a high impedanceto the line. The auxiliary winding 90 in the arrangement shown in FIG. 4is coupled as the secondary winding of a transformer to the mainwindings 92 and 93, and if it reflects a low impedance, it will causethe relay to act as a low impedance shunt for the speech signals, andadversely i I claim:

1. An electrical relay comprising a main winding, an auxiliary windingelectrically in series with said main winding and magnetically aiding,circuit means connecting a pair of normally open contacts across saidauxiliary winding so that said contacts are closed when the relay picksup.

2. An electrical relay comprising a main winding, an auxiliary windingelectrically in series with said mainv winding and magnetically aiding,a diode in series with said auxiliary winding, and a pair of normallyopen contacts connected across said auxiliary winding and said diode forshunting said auxiliary winding and said diode when the relay picks up.

3. An electrical circuit for use in conjunction with anelectromechanical actuator or the like to increase its sensitivitywithout correspondingly delaying its release characteristic comprising:

a. an auxiliary winding magnetically coupled to the core of theactuator; and

b. switching means for connecting said auxiliary winding in series withthe main winding of the actuator from the start of the application of anenergizing voltage until the actuator picks up, and for thereupon opencircuiting said auxiliary winding and closing a current path shunting itto apply the energizing voltage to the main winding only.

4. An electrical circuit according to claim 3 wherein said switchingmeans includes a transistor with its emitter-to-collector current pathin series with said auxiliary winding, and a pair of normally opencontacts arranged to close when the actuator picks up, said contactsbeing connected in shunt across said auxiliary winding and said currentpath of said transistor taken together.

5. A relay and associated circuit for use as a pulsing or battery feedrelay in a telephone switching system or the like d. two sets ofnormally open contacts respectively shunting said auxiliary windings andsaid transistors; and

e. means connecting the bases of said transistors respectively to thejunctions between said auxiliary windings and.

said main windings.

6. A relay according to claim 5, wherein the emitters of saidtransistors are connected to the terminals of a source of current, thecollectors are connected to said auxiliary windings, and the terminalsof said main windings opposite from said auxiliary windings are arrangedfor connection to a subscribers line or the like.

